Base station and method for receiving and processing signal in the base station

ABSTRACT

Disclosed is a method for simplifying a signal processing process of a base station that receives signals through four branches using two two-branch polarized antennas for each sector. The base station receives signals through first and second branches of the first polarized antenna and third and fourth branches of the second polarized antenna, time-delays the signals received at the second and fourth branches so as to distinguish an offset thereof from an offset of the signals received at the first and third branches, adds the signal received at the first branch and the signal received at the second branch and time-delayed, and adds the signal received at the third branch and the signal received at the fourth branch and time delayed. A modem processor separates an offset distinguishable signal from the added signals.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a method for receiving signals in amobile communication network, and a base station thereof. Morespecifically, the present invention relates to a method for reducingcomplexity of a base station when the base station uses two two-branchpolarization antennas to receive signals through four branches.

(b) Description of the Related Art

In general, signals transmitted from a mobile station antenna arereflected or refracted depending on environmental factors such as theground or buildings, and they are received to a base station antennathrough multiple paths. As described, when various signals are receivedthrough different paths, the signals undergo different amplitudeattenuations and phase changes. When the signals are combined, signalintensities change according to time variation differing from the signalintensities of transmission signals, which is referred to as fading. Tosolve the problem of fading, diversity methods for receiving variousindependently-faded signals and appropriately combining them have beenproposed.

The diversity methods include a space diversity method which is a methodof transmission by the simultaneous use of two or more physicallyseparated vertical antennas, and a polarization diversity method forseparately receiving vertical polarization and horizontal polarizationsignals. The polarization diversity method uses a polarized antenna todetect polarized signal components and uses them as branches ofdiversity.

Base stations based on the mobile communication systems such as IS-95,CDMA2000, and WCDMA generally use the space diversity method by usingtwo vertical antennas spatially separated for each sector to receivesignals. In this instance, the reason for using less than three antennasis that less merits are achieved compared to an increase of complexity.The above-noted mobile communication systems usually adopt thethree-sector method of using three sectors α, β, and γ. Referring toFIG. 5, a conventional configuration of a base station and a method forreceiving signals at the base station will be described.

FIG. 5 shows a conventional base station.

As shown, the conventional base station (e.g., a base station using thethree-sector method) includes RF/IF (radio frequency/intermediatefrequency) processors RF/IF1 through RF/IF6 for each antenna path. Thesignals received through the six vertical antennas are passed throughthe RF/IF processors to be converted into baseband signals, and areinput to a modem processor 20.

The modem processor 20 searches multipath signals for the six antennareception paths to allocate a valid multipath signal component to afinger, and detects a phase of the corresponding multipath signalcomponent to execute MRC (maximal ratio combining) on the signalcomponents allocated to the finger.

In detail, the two antennas in each sector are spatially separated toreceive signals with independent fading and phase, but they are not sofar from each other that spreading sequence offsets of the signalsreceived at the two antennas differ. Therefore, the signals that havethe same spreading sequence offset and different phase and fading arereceived through the two antennas, and the modem processor 20 performsphase detection and phase correction on these signals, and executes MRCto obtain a diversity effect. So as to achieve the diversity effect, itis required for the respective antenna components to maintainindependent signal paths without being added until MRC is executed onthem after the phase detection and phase correction.

Recently, a method using two sets of two branch X-pole antennas forenabling usage of both space diversity and polarization diversity hasbeen proposed. That is, when two sets of X-pole polarized antennas areprovided for each sector, the polarization diversity characteristics canbe obtained through the X-pole antennas, and since the two sets ofX-pole antennas are spatially separated, space diversity characteristicscan be obtained.

As shown in FIG. 6, in the two sets of two-branch X-pole antennas 41 and42, 43 and 44, and 45 and 46, each sector has four branches 41 a, 41 b,42 a, and 42 b; 43 a, 43 b, 44 a, and 44 b; and 45 a, 45 b, 46 a, and 46b. Accordingly, twelve RF/IF processors RF/IF1 through RF/IF12 coupledto each branch are to be formed in the base station (e.g., athree-sector base station), and a modem processor 50 having twelvereceivers for receiving signals from the twelve RF/IF processors is tobe used.

Hence, the number of the RF/IF processors and signal paths increase toincrease hardware complexity, and the conventional modem processor is tobe modified.

SUMMARY OF THE INVENTION

It is an advantage of the present invention to provide a base stationfor using two sets of X-pole polarized antennas without modifying amodem processor.

In one aspect of the present invention, a base station in a mobilecommunication network comprises: first and second polarized antennasrespectively having two branches and being formed in a same sector; afirst delay element for time-delaying a signal received at the secondbranch from among signals received at the first and second branches ofthe first polarized antenna so as to distinguish an offset of the signalfrom an offset of a signal received at the first branch; a second delayelement for time-delaying a signal received at the fourth branch fromamong signals received at the third and fourth branches of the secondpolarized antenna so as to distinguish an offset of the signal from anoffset of a signal received at the third branch; a first adder foradding the signal received at the first branch of the first polarizedantenna and a signal time-delayed by the first delay element; a secondadder for adding the signal received at the third branch of the secondpolarized antenna and a signal time-delayed by the second delay element;and a modem processor for receiving the signals added by the first andsecond adders and separating an offset distinguishable signal from therespective signals.

In this instance, it is preferable to locate RF and IF processorsbetween the first and second adder and the modem processor. The RF andIF processors may be located between the first and second antennas andthe first and second adders. The RF processor may be located between thefirst and second antennas and the first and second adders, and the IFprocessor may be located between the first and second adders and themodem processor.

In another aspect of the present invention, a method for receiving andprocessing signals at a base station in a mobile communication networkcomprises: receiving signals through first and second polarized antennasrespective having first and second branches and third and fourthbranches formed in the same sector; time-delaying the signals receivedat the second branch of the first polarized antenna and the fourthbranch of the second polarized antenna so as to distinguish offsets ofthe signals from offsets of signals received at the first and thirdbranches; adding the signal received at the first branch and the signalreceived at the second branch and time-delayed into a first add signal,and adding the signal received at the third branch and the signalreceived at the fourth branch and time-delayed into a second add signal;and separating an offset distinguishable signal from the first andsecond add signals.

In still another aspect of the present invention, a base station in amobile communication network comprises: a polarized antenna having firstand second branches; a delay element for time-delaying a signal receivedat the second branch of the polarized antenna so as to distinguish anoffset of the signal from an offset of a signal received at the firstbranch; an adder for adding the signal received at the first branch andthe signal received at the second branch and time-delayed by the delayelement; and a modem processor for considering an offset distinguishablesignal from the added signals as a different multipath signal, andseparating the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate an embodiment of the invention,and, together with the description, serve to explain the principles ofthe invention:

FIG. 1 shows a configuration of a base station according to a firstpreferred embodiment of the present invention;

FIG. 2 shows a difference of spreading sequence offsets caused by timedelay according to a first preferred embodiment of the presentinvention;

FIGS. 3 and 4 show configurations of a base station according to secondand third preferred embodiments of the present invention;

FIG. 5 shows a conventional configuration of a base station; and

FIG. 6 shows a conventional configuration of a base station using anX-pole polarization antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventor(s) ofcarrying out the invention. As will be realized, the invention iscapable of modification in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawings and descriptionare to be regarded as illustrative in nature, and not restrictive.

Referring to FIG. 1, a base station according to a first preferredembodiment of the present invention will be described.

FIG. 1 shows a configuration of a base station according to the firstpreferred embodiment of the present invention, and FIG. 2 shows adifference of spreading sequence offsets caused by time delay accordingto the first preferred embodiment of the present invention.

A base station in the mobile communication system adopting thethree-sector method will be exemplified below.

As shown in FIG. 1, the base station includes three sectors α, β, and γeach of which has two X-pole polarized antennas 110, 120, 130, 140, 150,and 160, each of which has two branches (the two branches arerespectively denoted as ‘a’ and ‘b’, and the reference numerals ‘a’ and‘b’ in the drawings represent the branches of each antenna). Theantennas 110, 120, 130, 140, 150, and 160 includes RF processors 310,320, 330, 340, 350, and 360, and IF processors 410, 420, 430, 440, 450,and 460 connected to a modem processor 500. In this instance, a singleRF processor 310, 330, and 350 and a single IF processor 410, 430, and450 for each sector perform a transmission function.

The X-pole polarized antenna is an antenna for realizing two-branchpolarization diversity, and two sets of X-pole antennas are provided foreach sector in the first preferred embodiment. The two X-pole antennasin each set are spatially separated to obtain the space diversityeffect, and two sets of the spatially separated two-branch polarizationdiversities can realize four branches.

Signals received at the four branches have independent phases andundergo independent fading, but the spreading sequence offsets of thesignals received through the branches at the same time frame areidentical. When the signals having the same spreading sequence offsetreceived at the branches are added before execution of phase correction,signal distortion occurs, and it becomes difficult for the modemprocessor to demodulate the signals.

In the first preferred embodiment, therefore, delay elements 210, 220,230, 240, 250, and 260 for delaying the signals received at one 110 b,120 b, 130 b, 140 b, 150 b, and 160 b of the two branches of thepolarized antenna are additionally formed between the branch 110 b, 120b, 130 b, 140 b, 150 b, and 160 b and the RF processor 310, 320, 330,340, 350, and 360. For example, as shown in FIG. 2, an additionalspreading sequence offset is provided to the signal delayed by the delayelement 210 from among the signals received at the two branches 110 aand 110 b of the antenna 110, and accordingly, the signals receivedthrough different branches at one polarized antenna have differentspreading sequence offsets.

In this instance, a time delay D assigned by the base station is to bedetermined such that the spreading sequence offsets of the multipathcomponents of branches without time delay are not superimposed on thespreading sequence offsets of the multipath components of branches withtime delay, and a time delay value is established according to amultipath delay profile. For example, since valid multipath componentsare received by the time delay of up to 25 μs in the worst case under awireless urban environment with heavy multipath delays, it is needed toassign the time delay D of about 25 μs to one of the two branches.

That is, when the time delay D of 30.72 chips (=25 μs×1.2288 MHz) isprovided in the case of using the spreading sequences of 1.2288 MHz, nospreading sequence offsets of valid multipath components receivedthrough branches without time delay are superimposed on the spreadingsequence offsets of valid multipath components received through brancheswith time delay.

The signals received at the branches 110 a, 120 a, 130 a, 140 a, 150 a,and 160 a without time delay and the signals received at the branches110 b, 120 b, 130 b, 140 b, 150 b, and 160 b with time delay are addedby an adder, and added signals are provided to the RF processors 310,320, 330, 340, 350, and 360. The RF processors 310, 320, 330, 340, 350,and 360 convert the signals into IF signals and provide the IF signalsto the IF processors 410, 420, 430, 440, 450, and 460. The IF processors410, 420, 430, 440, 450, and 460 convert the IF signals into basebandsignals, and provide the baseband signals to the modem processor 500.

Since the signals input to the modem processor 500 are signals addedwith distinguished spreading sequence offsets, these signals areprocessed in the same manner of signals input to the modem processor 500through different antennas and the RF/IF processing path. In detail,since the signals input to respective reception ends of the modemprocessor 500 are signals generated by adding the signals without timedelay and the signals with time delay and distinguishing the spreadingsequence offsets, a searcher of the modem processor 500 considers thesignals as various multipath components of the same antenna and dividesthe signals. The modem processor 500 allocates valid multipath signalcomponents to fingers, detects phases of the corresponding multipathsignal components to correct the same, and executes MRC on the signalcomponents allocated to the fingers. Other signals with different phasesare corrected to have the identical phase, and the MRC is performed onthe corrected signals, thereby obtaining the diversity effect.

In the first embodiment, two sets of X-pole polarized antennas spatiallyseparated for each sector are used, and since the X-pole polarizedantennas have two branches, signals can be received with four branchesper sector. In this instance, since one of the signals received at thetwo branches of each antenna is assigned a time delay, the signal andthe time delay are added, and the added result is transmitted to themodem processor, the modem processor needs to have two reception (Rx)ends for each sector. That is, since the modem processor used by theconventional base station, which has two vertical antennas for eachsector and each antenna has a branch, has two reception (Rx) ends foreach sector, the conventional modem processor can be applied to thepresent invention.

As described, since two RF processors and two IF processors are used persector in the first preferred embodiment, hardwired complexity does notincrease, and since two sets of X-pole polarized antennas are used toincrease the number of the diversity branches to four, theperformance-improved base station can be realized by the diversity. Butif the signals are delayed and added before they are input to the modemprocessor in the same manner of the first embodiment, performance may besomewhat degraded because of signal superimposition between parts ofweak components (i.e., the multipath components that are moretime-delayed than the artificially given time delay, and are received)from among multipath components received through an antenna to which noartificial time delay is given according to characteristics of multipathdelay, and important components from among artificially time delayedmultipath components, but this kind of performance degradationrelatively ignored compared to the diversity effect obtainable by usingtwo sets of the X-pole polarized antennas for each sector.

In order to avoid even the partial performance degradation, it isdesirable to process the modem processor through a separate path, whichdisadvantageously increases hardwired complexity caused by an increaseof the RF processors or the IF processors. Therefore, a base stationthat does not greatly increase its complexity and uses two sets ofX-pole polarized antennas thereby obtaining the diversity effect can berealized according to the first embodiment.

Other preferred embodiments of the present invention will be describedreferring to FIGS. 3 and 4.

FIGS. 3 and 4 show configurations of a base station according to secondand third preferred embodiments of the present invention.

As shown in FIG. 3, the base station according to the second preferredembodiment is matched with the first preferred embodiment except thatthe number of RF processors is different and the delay elements arelocated between the RF processors and the IF processors.

In detail, the signals received at the branches 110 a, 110 b, 120 a, 120b, . . . , 160 a, 160 b of the respective antennas 110 through 160 arerespectively transmitted to the RF processors 311, 312, 321, 322, . . ., 361, 362 and converted into IF signals. The signals passed through theRF processors 312, 322, . . . , 362 are delayed by delay elements 210,220, . . . , 260, and added, by an adder, with the signals passedthrough the RF processors 311, 321, . . . , 361. The added signals areconverted into baseband signals by the IF processors 410 through 460,and the baseband signals are transmitted to the modem processor 500.

According to the second preferred embodiment, the number of RFprocessors problematically becomes twice compared to the firstembodiment since the signals are added after passing through the RFprocessor.

A third embodiment for adding the signals passed through the RFprocessor will now be described referring to FIG. 4.

As shown in FIG. 4, the base station according to the third preferredembodiment is matched with the first preferred embodiment except thatthe number of RF processors and IF processors is different and the delayelements are located between the IF processors and the modem processor.

In detail, the signals received at the branches 110 a, 110 b, 120 a, 120b, 160 a, 160 b of the respective antennas 110 through 160 arerespectively transmitted to the RF processors 311, 312, 321, 322, . . ., 361, 362 and the IF processors 411, 412, 421, 422, . . . , 461, 462and converted into baseband signals. The signals passed through the IFprocessors 412, 422, . . . , 462 are delayed by delay elements 210, 220,. . . , 260, and added, by an adder, with the signals passed through theRF processors 411, 421, . . . , 461, and transmitted to the modemprocessor 500.

According to the third preferred embodiment, the number of RF processorsand IF processors problematically becomes twice compared to the firstembodiment since the signals are added after passing through the RFprocessor.

In the first to third preferred embodiments, the delay elements arerespectively provided between the antenna and the RF processor, betweenthe RF processor and the IF processor, and between the IF processor andthe modem processor to delay the signals and add delayed signals.However, without being restricted to this, the present inventionincludes a method for time-delaying the signals received through asingle branch of an antenna having two branches, adding the same withother signals without time delay received through another branch, andtransmitting the added signals to the modem processors.

According to the present invention, since time-delayed signals fordistinguishing offsets and time-undelayed signals are added, and theadded signals are divided by the modem processor, the diversity basestation using two sets of X-pole polarized antennas that require fourbranch processing for each sector without modifying the modem processorof the base station can be realized. That is, the hardwired modificationof the base station is minimized, IS thereby providing simple hardware.

While this invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not limited to thedisclosed embodiments, but, on the contrary, is intended to covervarious modifications and equivalent arrangements included within thespirit and scope of the appended claims.

1. A base station in a mobile communication network, comprising: firstand second polarized antennas respectively having two branches and beingformed in a same sector; a first delay element for time-delaying asignal received at the second branch from among signals received at thefirst and second branches of the first polarized antenna so as todistinguish an offset of the signal from an offset of a signal receivedat the first branch; a second delay element for time-delaying a signalreceived at the fourth branch from among signals received at the thirdand fourth branches of the second polarized antenna so as to distinguishan offset of the signal from an offset of a signal received at the thirdbranch; a first adder for adding the signal received at the first branchof the first polarized antenna and a signal time-delayed by the firstdelay element; a second adder for adding the signal received at thethird branch of the second polarized antenna and a signal time-delayedby the second delay element; and a modem processor for receiving thesignals added by the first and second adders and separating an offsetdistinguishable signal from the respective signals.
 2. The base stationof claim 1, further comprising: first and second RF (radio frequency)processors respectively connected to the first and second adders, forconverting the respective signals from the first and second adders intoIF (intermediate frequency) signals; and first and second IF processorsrespectively connected between the first and second RF processors andthe modem processor, for converting the respective signals from thefirst and second RF processors into baseband signals, and transmittingthe baseband signals to the modem processor.
 3. The base station ofclaim 1, further comprising: first through fourth RF processorsrespectively connected to the first through fourth branches, forconverting the respective signals from the first through fourth branchesinto IF signals, and respectively transmitting the IF signals to thefirst adder, the first delay element, the second adder, and the seconddelay element; and first and second IF processors connected between thefirst and second adders and the modem processor, for converting thesignals from the first and second adders into baseband signals, andtransmitting the baseband signals to the modem processor.
 4. The basestation of claim 1, further comprising: first through fourth RFprocessors respectively connected to the first through fourth branches,for converting the respective signals from the first through fourthbranches into IF signals; and first through fourth IF processorsrespectively connected between the first through fourth RF processors,the first adder, the first delay element, the second adder, and thesecond delay element, for converting the signals from the first throughfourth RF processors into baseband signals.
 5. A method for receivingand processing signals at a base station in a mobile communicationnetwork, comprising: (a) receiving signals through first and secondpolarized antennas respective having first and second branches and thirdand fourth branches formed in the same sector; (b) time-delaying thesignals received at the second branch of the first polarized antenna andthe fourth branch of the second polarized antenna so as to distinguishoffsets of the signals from offsets of signals received at the first andthird branches; (c) adding the signal received at the first branch andthe signal received at the second branch and time-delayed into a firstadd signal, and adding the signal received at the third branch and thesignal received at the fourth branch and time-delayed into a second addsignal; and (d) separating an offset distinguishable signal from thefirst and second add signals.
 6. The method of claim 5, wherein (c)further comprises respectively converting the first and second addsignals into baseband signals.
 7. The method of claim 5, wherein (a)further comprises converting the signals received at the first throughfourth branches into IF signals, and (c) further comprises respectivelyconverting the first and second add signals into baseband signals. 8.The method of claim 5, wherein (a) further comprises converting thesignals received at the first through fourth branches into basebandsignals.
 9. A base station in a mobile communication network,comprising: a polarized antenna having first and second branches; adelay element for time-delaying a signal received at the second branchof the polarized antenna so as to distinguish an offset of the signalfrom an offset of a signal received at the first branch; an adder foradding the signal received at the first branch and the signal receivedat the second branch and time-delayed by the delay element; and a modemprocessor for considering an offset distinguishable signal from theadded signals as a different multipath signal, and separating the same.